1. Field of Invention
The present invention relates to methods for making thin film patterns using chemical vapor deposition (CVD).
2. Description of Related Art
In chemical vapor deposition (CVD), the material for the thin film is fed in a gaseous form to a substrate, and the gas is decomposed by heat, light, etc., so that a desired thin film is deposited on or over the substrate. This process is widely used as a method for making thin films, for example, semiconductor films, insulating films, and conductive films, in the process of manufacturing semiconductor apparatus. In the CVD process, a vaporized substance that is obtained by vaporizing a liquid may be used as a raw material. The CVD process using organometallic compounds is particularly referred to as xe2x80x9cmetal organic chemical vapor depositionxe2x80x9d (MOCVD). In general, the gaseous materials and the vaporized substances of liquid materials are produced outside of a reaction chamber and are introduced into the reaction chamber via pipes.
In the process of manufacturing semiconductor apparatus, after a thin film is formed over the entire surface of a substrate, a patterning step is performed in which unnecessary parts are removed, leaving necessary parts of the thin film. The patterning step is usually performed as follows. First, a resist film is formed on the thin film, and the resist film is then irradiated with light through a photomask to form a resist pattern. Unnecessary parts of the thin film are then removed by etching using the resist pattern as a mask. Next, the resist pattern is removed.
Additionally, since CVD deposition is accompanied with a chemical reaction, it is also possible to only form a thin film in necessary regions (selective growth) by bringing about an inactive state in regions in which the thin film is unnecessary on the substrate.
However, in the conventional CVD and MOCVD processes, since hazardous gases which are highly reactive are introduced into a reaction chamber, leakage of the gases from the reaction chamber must be prevented during reaction, and the gases must be reliably recovered after the reaction. For this purpose, in a conventional CVD system and MOCVD system, large-scale vacuum exhaust units are provided. A portion of the gas introduced into the reaction chamber is subjected to reaction to form a thin film, and most of the gas must be recovered and neutralized.
As described above, since a method for making thin films using the conventional CVD process requires a large-scale vacuum exhaust unit or neutralization unit, there is room for a reduction in costs.
In particular, with respect to large liquid crystal displays, etc., an array of switching elements for corresponding pixels must be formed on a large area substrate, and if the array is formed by the conventional method (in which the patterning step is performed after the thin film is formed over the entire surface of the substrate), the amount of the thin film that is left on the substrate is significantly small, and most of the thin film is removed in the patterning step.
Additionally, even where the thin film is selectively grown using a CVD process, under the existing conditions, a step is required in which portions protruding from the pattern of the thin film are removed. That is, although the amount of the thin film to be removed can be decreased by selectively growing the thin film using the CVD process, even in such a case, it is still necessary to remove the unnecessary thin film after the thin film is formed.
As described above, in the method for producing large liquid crystal displays, etc., using the method for forming thin films using the conventional CVD process, the raw materials for the thin films are wasted, which is disadvantageous.
On the other hand, Japanese Unexamined Patent Application Publication No. 2000-12465 discloses a method for simultaneously forming silicon films on both film formation surfaces of a first member for forming the silicon film and a second member for forming the silicon film. In this method, the first member for forming the silicon film, in which a liquid raw material is applied on the film formation surface, and the second member for forming the silicon film are placed so as to face each other.
In accordance with this method, a silicon film is formed on the film formation surface of the first member for forming the silicon film by a decomposition reaction of the liquid raw material applied, and a silicon film is formed on the film formation surface of the second member for forming the silicon film by a decomposition reaction of a vaporized substance from the liquid raw material on the film formation surface of the first member for forming the silicon film. According to this publication, the simultaneous formation of silicon films on two substrates, and the formation of the silicon film with a uniform thickness over the entire surface of the second member for forming the silicon film, are mentioned as advantages of the invention.
However, in the method according to this publication, a patterning step must also be performed after the formation of the thin films in order to obtain a silicon thin film with a predetermined pattern.
The present invention addresses the problems associated with the conventional techniques described above. Thus, the present invention provides a method for forming a thin film using a CVD process in which a large-scale vacuum exhaust unit or neutralization unit is not required, and the thin film can be formed partially on a substrate using a small amount of raw material liquid. The invention also provides a method in which a thin film pattern is obtained, even without performing a patterning step after the formation of the thin film.
In order to address the problems described above, the present invention provides a method for forming a thin film using chemical vapor deposition, in which a liquid containing a raw material for the thin film is placed on a part or a plurality of parts of a substrate, and the raw material for the thin film is vaporized from the liquid so as to be fed to a part or a plurality of parts of the surface for forming the thin film, and thereby the thin film is formed with a predetermined pattern on the surface for forming the thin film.
In one aspect of the present invention, a method for forming a thin film by chemical vapor deposition includes the steps of: placing a liquid containing a raw material for the thin film on a part or a plurality of parts of a substrate; and vaporizing the raw material for the thin film from the liquid so as to be fed to a part or a plurality of parts of the surface for forming the thin film to form the thin film with a predetermined pattern on the surface for forming the thin film.
In accordance with this method, even where a thin film pattern in which a thin film is present on a significantly small part of a large area substrate is formed, the amount of the raw material for the thin film to be used can be significantly decreased. Additionally, since it is not necessary to introduce the raw material for the thin film in the gaseous state into a reaction chamber, a large-scale vacuum exhaust unit or neutralization unit is not required.
Examples to perform such a method are described below.
(1) In the method for forming the thin film, one surface of the substrate is used as a surface to place the liquid, and the thin film is formed in a region other than the region in which the liquid is placed on the surface to place the liquid.
In accordance with the method described above, by only using a substrate to form a thin film, without using a dummy substrate to place a liquid, it is possible to form a thin film pattern on the substrate.
(2) In the method for forming the thin film, a first substrate to place the liquid and a second substrate to form the thin film are placed so that the surface to place the liquid of the first substrate faces the surface to form the thin film of the second substrate, and the raw material for the thin film is vaporized from the liquid placed on a part or a plurality of parts of the first substrate so as to be fed to the surface to form the thin film of the second substrate.
Consequently, the thin film pattern can be formed on a part or parts of the surface to form the thin film of the second substrate facing the part or parts of the first substrate to place the liquid.
(3) In the method for forming the thin film, preferably, the surface to form the thin film of the second substrate is heated to a temperature at which a vaporized substance of the raw material for the thin film is decomposable, and the first substrate is heated to a temperature at which the raw material for the thin film is vaporized from the liquid by the heat radiated from the second substrate.
Consequently, the costs associated with the method using two substrates can be reduced.
(4) In the method for forming the thin film, before the step of placing the liquid, an active region and an inactive region for the chemical vapor deposition are formed in the surface to form the thin film so that the thin film is selectively deposited.
(5) In the method for forming the thin film, the formation of the active region and the inactive region for the chemical vapor deposition is performed by forming a self-assembled film on the surface to form the thin film having hydroxyl groups using a silane derivative represented by the general formula RSiX3 (where R is a fluoroalkyl group in which terminal hydrogen of the alkyl group is replaced with fluorine, and X is an alkoxy group or halogen group); and performing ultraviolet irradiation on the self-assembled film through a photomask or performing electron beam irradiation on necessary parts of the self-assembled film so that the self-assembled film in a region to form the active region for the chemical vapor deposition is removed.
Consequently, since the thin film pattern is obtained simultaneously with the formation of the thin film, a patterning step is not required after the formation of the thin film.
In the present invention, the xe2x80x9cself-assembled filmxe2x80x9d is a monolayer formed by making a compound, in which functional groups that are capable of linking to constituent atoms of a surface to form a film are combined with straight chain molecules, coexist in the gaseous or liquid state with the surface to form the film so that the functional groups are adsorbed on the surface to form the film to link to the constituent atoms, the straight chain molecules being directed outward. Since the monolayer is formed by spontaneous chemisorption of the compound to the surface to form the film, it is referred to as xe2x80x9ca self-assembled film.xe2x80x9d
Additionally, the self-assembled film is described in detail in Chapter 3 of A. Ulman, xe2x80x9cAn Introduction to Ultrathin Organic Film from Langmuir-Blodgett to Self-Assemblyxe2x80x9d (Academic Press Inc., Boston, 1991).
Where the gaseous or liquid silane derivative (RSiX3) is made to coexist with the surface to form the thin film in which hydroxyl groups are present, first, X is hydrolyzed by the moisture in the air to form a fluoroalkylsilanol (RSi(OH)3). Siloxane bonds are formed due to the dehydration reaction between the hydroxyl groups of the silanol anid the hydioxyl groups of the surface to form the film, and a monolayer (self-assembled film) in which the fluoroalkyl groups (R) are directed outward is formed on the surface to form the film. The surface of the self-assembled film is in an inactive state (with low surface energy and low reactivity) due to the presence of the fluoroalkyl groups.
Preferred examples of the silane derivative represented by the general formula RSiX3 are fluoroalkylalkoxysilanes, such as (heptadecafluoro-1,1,2,2-tetrahydro)decyl-triethoxysilane, (heptadecafluoro-1,1,2,2-tetrahydro)decyl-trimethoxysilane, (tridecafluoro-1,1,2,2-tetrahydro)octyl-trimethoxysilane, and (tridecafluoro-1,1,2,2-tetrahydro)octyl-triethoxysilane).
Accordingly, the portion of the surface to form the thin film, in which the self-assembled film is removed by the method described above, becomes an active region for the chemical vapor deposition, and the portion of the surface to form the thin film, in which the self-assembled film remains, becomes an inactive region for the chemical vapor deposition.
(6) In the method for forming the thin film, the step of vaporizing the raw material for the thin film is performed while supplying inert gas, hydrogen gas, or a mixture of inert gas and hydrogen gas parallel to the surface to place the liquid of the substrate.
Consequently, where a liquid is placed on the surface of the substrate to form the thin film, the vaporized substance from the liquid placed can be easily scattered in the vicinity of the position in which the liquid is placed. In the case that two substrates are used and the vaporized substance from the liquid placed on the first substrate is sent to the second substrate, it is possible to control the amount of the vaporized substance to be sent to the second substrate. Thereby, the thickness of the thin film to be formed can be controlled.
(7) In the method for forming the thin film, preferably, the step of placing the liquid is performed by an ink-jet method. As the liquid (liquid containing the raw material for the thin film) used in the method of the present invention, any liquid is acceptable as long as the raw material for the thin film is vaporized. Known liquid materials (e.g., liquid organometallic compounds and liquid silane compounds) which are used in a CVD or MOCVD process in general may be used.
Specific examples of organometallic compounds include trimethylaluminum, trimethylgallium, trimethylphosphine, and triethylaluminum. Specific examples of silane compounds include hydrogenated silane compounds, such as trisilane, tetrasilane, pentasilane, and hexasilane; halogenated silane compounds, such as tetrachlorosilane and trichlorosilane; the fluoroalkylalkoxysilanes; silane coupling agents represented by the general formula RnSiX(4xe2x88x92n); and tetraethoxysilane (TEOS).
In the methods of the present invention, as substrates (the substrate on which both the placement of the liquid and the formation of the thin film are performed, the first substrate on which only the placement of the liquid is performed, and the second substrate on which only the formation of the thin film is performed), silicon (Si) wafers, quartz plates, glass plates, plastic films, metal plates, or the like may be used. Such substrates on which semiconductor films, metal films, dielectric films, organic films, etc., are deposited may be used as substrates.
(8) In an electronic apparatus, thin films that are formed by any one of the methods for forming thin films described above can be used as electrodes.